A computed tomography (CT) apparatus is an apparatus for imaging the inside of an object by scanning the object using radiation, etc. and processing the acquired data using a computer. Some examples of CT apparatuses include: an X-ray CT apparatus, PET (Positron Emission Tomography), SPECT (Single Photon Emission Computed Tomography), an MRI (Magnetic Resonance Imaging) apparatus, etc.
The computed tomography apparatus comprises a gantry, a couch, a console, etc. The gantry is provided with an opening in the center region thereof. A subject placed on the couch is moved into the inside of the opening and subjected to an examination. At that time, a light beam from a projector provided in the gantry is used to estimate the body axis of the subject in order to perform determination of the position of the center of the opening and the subject (determination of the position of an imaging region).
Furthermore, a field of view is set when conducting computed tomography imaging. The “field of view” is the region in which imaging by a computed tomography apparatus is possible. Because the field of view varies depending on the imaging conditions (imaging region, etc.), in general, several fields of view are preliminarily set and stored for each apparatus. The field of view preferably covers the entire imaging region (for example, a head or a torso) including a region of interest of the subject. Moreover, by setting the range of the field of view to be approximately the same size as the imaging region of the subject, imaging with high resolution becomes possible with the apparatus.